Water Tank Air Pre-Charge Pressure FAQs

Adjust the air pressure if you change the pressure switch
Air leaks out of the pressure tank, loses charge
Wrong air charge effect on the pump prime?

Can the Wrong Water Pressure Tank Charge Cause Loss of Pump Prime?

Can an improper water tank air pre-charge cause loss of well pump prime?

My pressure tank gauge shows 30 psi when it’s pumping however it loses it’s prime every now and then I’ve been told it doesn’t have enough air in it I installed everything new but didn’t realize I had to add air to it could thus be the reason its losing prime? On 2021-01-11 by David

Reply by (mod) - No

No, David; the water pressure tank itself nor its air pre-charge amount would not explain loss of pump prime. The loss of pump prime in a well pump - by which I think you refer to an aboveground one-line or two-line jet pump, happens because a check valve, either at the pump or in the well (a foot valve) is leaking, allowing water to drain back out of the pump and into the well when the pump is off for a time.

You'll want to read the troubleshooting and repair procedure we give at PUMP PRIME, REPEATED LOSS  - DF.

Loss of Air Charge in Bladder Type Water Pressure Tanks

Water Pressure Tank Loses Air Pressure - where's the leak?

I suspected the pressure of my tank was low. I shut off power to the pump and opened the faucet until the water stopped and gauge near tank read zero pressure.

I then checked the bladder pressure and it was 31. I have a 40-60 system. So I set the bladder pressure to 38 and adjusted to cut in and cut out to exactly 40 and 60.

Good to go for several months, then thought my water pressure was on the low side again.

Checked the bladder pressure and sure enough it was 32 this time. I left it as is for now. I tried putting soap around the top Schrader valve but I did not see any bubbles.

If I have a leak it must be real slow one.

Any ideas am I missing anything? Really appreciate any guidence you can provide. 2019-02-12 by Phil

by (mod) - yes there's an air leak somewhere

That sounds like you did just the right adjustment.

Keep in mind there can be other leaks that you can't see directly: leaks in well piping, a leaky foot valve or check valve, and even subtle leaks on the pump itself.

But if your water pressure tank is one that uses an internal bladder then I suspect that the air leak is at the tank itself or at its air valve, the Schrader valve.

The little valve insert or pin in a Schrader valve can be replaced. You might try that to see if cleaning the valve stem and replacing the valve core works to stop the leak.

For other readers: a sign that the air charge may have been lost OR that the water tank bladder is leaking or damaged would be water pump short cycling, described along with repair advice

at WATER PUMP SHORT CYCLING

More about repairing leaky water tanks is

at WATER TANK REPAIR PROCEDURES 

and WATER TANK LIFE & REPLACEMENT

Adjust Water Tank Air Pre-Charge If you Change the Pressure Control Switch

Can I re-set a 30/50 pressure switch down to 20/40?

I have a Well-X-trol WX203, which comes preset 28 psi and a pump switch 30/50. May I change the recommended 30/50 pump switch to a 20/40 and accordingly adjust the air pressure to 18 psi? On 2016-08-02 by BillM

by (mod) - yes but remember to adjust the pressure tank's air-charge

The Well-X-Trol WX203 is a newer Amtrol product.

Your model, #203, is a 32 gallon tank. At 30/50 pumping range you're getting about ten gallons of draw-down before the pump has to turn on.

The product chart shows draw-down quantities for various tank sizes at three pressure ranges: 30/50, 40/60, 50/70 psi.

The tank will work with a lower operating range of 20/40 but the draw-down quantity will probably be reduced by a bit over 10% or to about 9 gallons.
That means the pump will run 10% more often - probably not a catastrophe. You will also see the the flow rate at fixtures (what people call "water pressure") will be a bit less.

I'd give it a try. But

Watch out: the proper water tank air pre-charge (with the tank empty of water) for a 30/50 pressure control is (30 - 2 ) or 28 psi.

When you lower the pressure control switch down to 20/40 that drops the CUT-IN pressure to 20 psi at the switch. So you need to adjust the water tank air pre-charge down to (20 - 2) or 18 psi.

If you don't do that the pump will never turn on.

What will happen if the tank pressure is set above the pump cut-in?

Just bought a new pressure tank with the pre-set stated as 28 psi which is correct for my cut-in of 30psi.

But a check with 2 pressure gauges shows it is 34 psi. I either accept the factory pre-set as correct and my gauges read high or my gauges are correct and I release air. 2 psi is not much of a margin-of-error. What will happen if the tank pressure is set above the pump cut-in? (Oct 25, 2015) Colin

Reply: the pump will never turn on

Colin

Keep in mind that the air pressure you read at a water tank will be affected by temperature changes. If your water or tank are warm the pressure will be high.

I would go ahead and drop the pressure to 28 psi by your gauges.

If you set the air pressure in the tank above the pump's cut-in pressure with a tank using an internal bladder, ultimately the pump won't turn on.

In a tank that does not separate air from water by using an internal bladder, the excess air will simply blow out of nearby faucets and thus the problem will resolve itself.